WPF UserControl is not drawn when overriding MeasureOverride and ArrangeOverride

I have a UserControl looking like this:

<UserControl
    MaxHeight="32"
    MaxWidth="32"
    MinHeight="25"
    MinWidth="25">
    <DockPanel>
        <!-- some stuff -->
    </DockPanel>
</UserControl>

In addition to the min/max size constraint, I want the control always being painted with Width = Height. So i override Me开发者_高级运维asureOverride and ArrangeOverride:

protected override Size MeasureOverride(Size availableSize)
{
    var resultSize = new Size(0, 0);
    ((UIElement)Content).Measure(availableSize);
    var sideLength = Math.Min(((UIElement)Content).DesiredSize.Width, ((UIElement)Content).DesiredSize.Height);

    resultSize.Width = sideLength;
    resultSize.Height = sideLength;

    return resultSize;
}

protected override Size ArrangeOverride(Size finalSize)
{
    ((UIElement)Content).Arrange(new Rect(0, 0, finalSize.Width, finalSize.Height));
    return finalSize;
}

I understand that I must call Measure and Arrange on every child of the UserControl. Since the DocPanel is the only child of my UserControl and (in my understanding) is stored in the Content property of the UserControl, I simply call Measure and Arrange on this Content property. However the UserControl is not displayed. What am I doing wrong?

Depending on how you are hosting your UserControl, the value returned from the Measure phase may not be used. If you have it setup in a Grid with star rows/columns or a DockPanel, then the final size may be completely different.

You would need to apply similar logic to the arrange phase, so it will effectively ignore any extra space it's given.

The following code should work, and is a bit cleaner:

protected override Size MeasureOverride(Size availableSize) {
    var desiredSize = base.MeasureOverride(availableSize);
    var sideLength = Math.Min(desiredSize.Width, desiredSize.Height);

    desiredSize.Width = sideLength;
    desiredSize.Height = sideLength;

    return desiredSize;
}

protected override Size ArrangeOverride(Size finalSize) {
    var sideLength = Math.Min(this.DesiredSize.Width, this.DesiredSize.Height);
    return base.ArrangeOverride(new Size(sideLength, sideLength));
}